Studies in ion solvation in non-aqueous solvents and their aqueous mixtures. Part 20.—Enthalpies of transfer of alkali-metal halides in the methanol + water system from enthalpies of dilution

Abstract

Enthalpies of transfer, ΔH⁰_t, of the alkali-metal chlorides and of sodium bromide and sodium iodide from water to methanol + water mixtures over the whole range of solvent composition have been determined by measuring heats of dilution of concentrated aqueous solutions. Greater precision is achieved than when heats of solution are measured. A submarine calorimeter was used and the concentrated solutions injected with a dispensing pipette. This gave precise results rapidly.

Results for sodium chloride obtained by measuring heats of solution were in good agreement with those from heats of dilution. There is fair agreement with the classical work of Slansky except for Li⁺Cl^–.

Comparison with ΔG⁰_t and ΔS⁰_t confirms that ΔG⁰_t is the simplest function and suggests that structural effects compensate in ΔH⁰_t and ΔS⁰_t.